Lightning current transfer assembly for a wind turbine

Abstract

A lightning current transfer assembly ( 2 ) for a wind turbine ( 1 ) is arranged to transfer lightning current from a wind-turbine part ( 8 ) to another part ( 8 ) rotatable relative to it. The assembly comprises at least one electric contact arrangement ( 11′, 11 ″) comprising complementary contact members ( 12 a′, 12 b′, 12 a″, 12 b ″) which provide electric connection by mechanically contacting each other while being movable relative to each; a spark gap ( 4 ) connected in series with the movement-enabling contact arrangement ( 11′, 11 ″); and a spark-gap-bridging resistance ( 6 ) connected parallel to the spark gap ( 4 ). Thereby, the assembly provides at least two alternative current paths: (i) a lightning current path across the at least one electric contact arrangement and the spark gap, and (ii) a permanent-discharge current path across the at least one electric contact arrangement and through the spark-gap-bridging resistance.

The invention claimed is: 
     
       1. A lightning current transfer assembly for a wind turbine comprising at least a first part and a second part rotatable relative to each other, the lightning current transfer assembly being arranged to transfer lightning current from the first part to the second part, comprising:
 at least one electric contact arrangement comprising complementary contact members which provide electric connection by mechanically contacting each other while being movable relative to each other; 
 a spark gap connected in series with the at least one electric contact arrangement, wherein the spark gap comprises spark-gap electrodes, the spark-gap electrodes being stationary relative to each other; and 
 a spark-gap-bridging resistance connected parallel to the spark gap, 
 the lightning current transfer assembly thereby providing at least two alternative current paths from the first part to the second part: 
 (i) a lightning current path across the at least one electric contact arrangement and the spark gap, and 
 (ii) a permanent-discharge current path across the at least one electric contact arrangement and through the spark-gap-bridging resistance. 
 
     
     
       2. The lightning current transfer assembly of  claim 1 , wherein the spark-gap-bridging resistance comprises one or more resistors. 
     
     
       3. The lightning current transfer assembly of  claim 1 , wherein the complementary contact members of the at least one electric contact arrangement comprise a contact slider or roller and a complementary ring or belt contacted by the contact slider or roller. 
     
     
       4. The lightning current transfer assembly of  claim 1 , the lightning current transfer assembly being arranged to transfer lightning current between first and second parts rotatable relative to each other around two different axes, the lightning current transfer assembly comprising at least two electric contact arrangements connected in series. 
     
     
       5. The lightning current transfer assembly of  claim 4 , wherein the spark gap and the spark-gap-bridging resistance are interposed between the at least two electric contact arrangements, thereby forming a series connection of a first electric contact arrangement, the spark gap, the parallel connection of the spark gap and the spark gap bridging resistance, and a second electric contact arrangement. 
     
     
       6. The lightning current transfer assembly of  claim 4 , wherein
 the lightning current transfer assembly is arranged for mounting on a wind turbine comprising at least one rotor blade, a rotor hub, and a nacelle, the rotor blade being rotatable relative to the rotor hub around a first axis, and the rotor hub being rotatable relative to the nacelle around a second axis, 
 the lightning current transfer assembly comprising a lightning current transfer unit arranged to be mounted on the rotor hub, 
 wherein the lightning current transfer assembly provides a lightning current path and a permanent-discharge current path from the rotor blade to the nacelle by means of the at least two electric contact arrangements, connected in series with the parallel connection of the spark gap and the spark-gap-bridging resistance interposed. 
 
     
     
       7. The lightning current transfer assembly of  claim 6 , wherein both the galvanically discontinuous lightning current path and the permanent-discharge current path through the lightning current transfer unit are electrically isolated from the rotor hub, so that lightning current bypasses the rotor hub and rotation-enabling bearings between the rotor blade and the rotor hub and between the rotor hub and the nacelle. 
     
     
       8. The lightning current transfer assembly of  claim 4 , wherein the at least two electric contact arrangements are connected by a wire, the spark gap being interposed in the wire connection between the at least two electric contact arrangements. 
     
     
       9. The lightning current transfer assembly of  claim 1 , wherein the spark gap is mounted on an isolating stand. 
     
     
       10. The lightning current transfer assembly of  claim 1 , comprising a base support made of insulating material which is a common support of both the spark gap and at least one of the contact members. 
     
     
       11. The lightning current transfer assembly of  claim 10 , wherein the at least one of the contact members is pivotally mounted on the base support or to a member fixed to the base support. 
     
     
       12. The lightning current transfer assembly of  claim 1 , wherein the spark gap is encapsulated, the encapsulation allowing air to escape, but preventing particles produced when a spark occurs from escaping. 
     
     
       13. The lightning current transfer assembly of  claim 12 , wherein the spark gap encapsulation comprises a mesh surrounding the spark gap. 
     
     
       14. The lightning current transfer assembly of  claim 12 , wherein the spark gap encapsulation comprises a labyrinth-shaped housing. 
     
     
       15. The lightning current transfer assembly of  claim 12 , wherein the spark gap encapsulation is at least partially made of electrically conductive material and forms part of the permanent-discharge current path bridging the spark gap and including the spark-gap-bridging resistance. 
     
     
       16. A wind turbine, comprising:
 at least one lightning current transfer assembly comprising at least a first part and a second part rotatable relative to each other, the lightning current transfer assembly being arranged to transfer lightning current from the first part to the second part, comprising: 
 at least one electric contact arrangement comprising complementary contact members which provide electric connection by mechanically contacting each other while being movable relative to each other; 
 a spark gap connected in series with the at least one electric contact arrangement, wherein the spark gap comprises spark-gap electrodes, the spark-gap electrodes being stationary relative to each other; and 
 a spark-gap-bridging resistance connected parallel to the spark gap, 
 the lightning current transfer assembly thereby providing at least two alternative current paths from the first part to the second part: 
 (i) a lightning current path across the at least one electric contact arrangement and the spark gap, and 
 (ii) a permanent-discharge current path across the at least one electric contact arrangement and through the spark-gap-bridging resistance.